On Thu, 1 Dec 2022 15:33:17 -0800 Mina Almasry <almasrymina@xxxxxxxxxx> wrote: > Reclaiming directly from top tier nodes breaks the aging pipeline of > memory tiers. If we have a RAM -> CXL -> storage hierarchy, we > should demote from RAM to CXL and from CXL to storage. If we reclaim > a page from RAM, it means we 'demote' it directly from RAM to storage, > bypassing potentially a huge amount of pages colder than it in CXL. > > However disabling reclaim from top tier nodes entirely would cause ooms > in edge scenarios where lower tier memory is unreclaimable for whatever > reason, e.g. memory being mlocked() or too hot to reclaim. In these > cases we would rather the job run with a performance regression rather > than it oom altogether. > > However, we can disable reclaim from top tier nodes for proactive reclaim. > That reclaim is not real memory pressure, and we don't have any cause to > be breaking the aging pipeline. > Is this purely from code inspection, or are there quantitative observations to be shared?
